Theoretical studies on metal thioarsenites and thioantimonides: synergistic interactions between transition metals and heavy metalloids

• Main Author: Tossell JA
• Format: Article
• Language: English
• Published: BMC 2000-05-01
• Series: Geochemical Transactions
• Online Access: http://dx.doi.org/10.1186/1467-4866-1-16

<p/> <p>Recently we established that the ternary complex, CuAsS(SH)(OH) has an unusually high stability and makes a large contribution to the total concentrations of both Cu and As in sulfidic solutions equilibrated with Cu and As sulfide minerals. This ternary complex has an unusual structure, containing a bond which is formally Cu(I)–As(III), along with a broken As–S bond. We have now found that complexes with similar structures exist for Au⁺and Tl⁺coordinated to AsS(SH)(OH)^-. However, such a direct metal–metalloid bond is not a requirement for stability. In fact, TlAsS(SH)(OH) is unstable while AuAsS(SH)(OH) is highly stable (compared to the aquo ion). Zn²⁺, Cd²⁺, Hg²⁺and Pb²⁺also form bonds to the As of AsS(SH)(OH), but without breaking any As–S bonds, and HgAsS(SH)(OH)⁺and PbAsS(SH)(OH)⁺are particularly stable complexes. Calculated structures are shown for these complexes, gas-phase energies are calculated, and formation constants in aqueous solution are estimated. The SbS(SH)(OH)^-ion forms analogous complexes, with similar stabilities. However, the Au⁺complex of SbS(SH)(OH)^-is slightly less stable than the Cu⁺complex, opposite to the order found for the AsS(SH)(OH)^-ligand. The Au⁺and AuSH complexes of AsSSHOH^-or AsS(SH)₂^-may be implicated in "invisible gold" in arsenian pyrites. Vibrational frequencies are given for the AuAsS(SH)₃^-complex and the XANES energies of this complex and Au(SH)₂^-are compared. The existence of such strong complexes may explain the many correlations observed between the concentrations of coinage metals and metalloids.</p>